1. Field of the Invention
The present invention relates to an apparatus for supporting a tiltable steering shaft which, with a very simple structure, is capable of demonstrating impact absorbing action speedily and reliably with respect to an impact occurring during a collision.
2. Description of the Related Art
Various apparatuses for supporting tiltable steering shafts have been proposed in which, in the event that an impact load has acted upon a steering wheel by the driver during a collision of a vehicle, a mounting portion of a fixed bracket is disengaged from a vehicle body-side mounting portion, so as to ensure the driver's safety. For example, in an apparatus disclosed in Japanese Utility Model Application Laid-Open No. 64-42970, a stopper member is formed on the fixed bracket so as to abut against the steering column for restricting the rotation of the fixed bracket when the driver has hit against the steering wheel during a collision of a vehicle, and an impact load has acted upon the steering column.
Among such stopper members, there is one which is formed by also serving as a connecting member for connecting a right side plate and a left side plate of the fixed bracket, and there is another in which both side end portions of an upper mounting portion of the fixed bracket are bent in such a manner as to oppose each other, as shown in Japanese Utility Model Application Publication No. 4-50218.
In addition, as disclosed in Japanese Utility Model Application Publication No. 4-43420, there is an apparatus in which a stopper member, which abuts against an end of a fixed bracket when an impact load has acted upon the steering column, is formed on a movable bracket, the stopper member being formed integrally in such a manner as to project laterally from both sides at one end of the movable bracket.
In these apparatuses, the stopper members are not newly attached as separate parts, but they are each formed by bending a component part of the apparatus or by making such a component part serve a double purpose. Hence, since the number of component parts used does not increase, and the structures are relatively simple, the apparatuses can be made compact.
In the above-described stopper members, the rotation of the fixed bracket due to the angular moment acting in the clockwise direction about a tilting bolt when the impact load acts is prevented as the stopper member comes into contact with the steering column or the movable bracket. With the apparatuses for supporting a tiltable steering shaft in the above-described conventional examples, in addition to the rotation of the fixed bracket, bending moment acts about attaching bolts in the mounting portion of the fixed bracket, and a portion of the bracket close to the attaching bolts becomes deformed, thereby possibly making it difficult for the bracket to be disengaged from the mounting portion of the vehicle body.
Among the above-described conventional examples, the stopper member, which also serves as the connecting member and is adapted to abut against the steering column and is disposed on the mounting portion of the fixed bracket as in Japanese Utility Model Application Laid-Open No. 64-42970, is formed of a thin plate, and its end face is set as an abutment surface against the steering column so that its cross section taken along the abutting direction is made large. Hence, the rigidity in the abutting direction only is secured, and the stopper member essentially serves as a connecting member for connecting the left and right side plates.
Such a stopper member is provided on the front side (steering wheel side) of the mounting portion of the fixed bracket and in the vicinity of the mounting portion of the bracket. When the aforementioned bending moment acts, a substantially large force is received in the vicinity of the mounting portion of the fixed bracket due to the bending moment in the mounting portion of the fixed bracket. Thus, there is a possibility that the stopper member becomes deformed, so that the deformation of the mounting portion of the fixed bracket cannot be prevented, thereby making it impossible for the bracket to be disengaged smoothly from the mounting portion of the vehicle body.
Hence, although the above-described stopper member also serves as the connecting member for connecting the left and right side plates, in the final analysis the stopper member only restricts the rotation of the fixed bracket due to its abutment against the steering column, and cannot prevent the deformation due to the bending moment applied to the mounting portion of the fixed bracket.
In addition, with the structure for restricting the rotation by abutment between the steering column and the stopper member provided on the fixed bracket as in the cases of Japanese Utility Model Application Laid-Open No. 64-42970 and in Japanese Utility Model Application Publication No. 4-50218, the distance between the steering column and the stopper member formed on the fixed bracket varies depending on the vertically adjusted position of the tiltable steering column. Hence, there is a problem in that it is difficult to obtain stable abutment by setting the timing of abutment against the steering column.
The above-described apparatus disclosed in Japanese Utility Model Application Publication No. 4-43420 has a U-shaped cross section in which the mounting portion side of the fixed bracket is open, and lower portions of the side plates of the bracket are connected integrally. Since the flexural rigidity of the mounting portion of the fixed bracket is not necessarily secured, in the event that bending moment has acted about the attaching bolts, it is impossible to sufficiently prevent the deformation of the mounting portion of the bracket close to the attaching bolts, thereby possibly making it difficult for the bracket from being disengaged smoothly from the mounting portion of the vehicle body.
In addition, if the stopper member is formed integrally at one end of the movable bracket as described above, since the tilting bolt where the center of angular moment is formed is located in the movable bracket, and the stopper member is formed at a substantially shortest distance from the tilting bolt with respect to the vertically adjusting position of the steering column, there is the possibility of the amount of rotation of the fixed bracket becomes large until the fixed bracket abuts against the stopper member. As a result, there is a problem in that it is difficult to restrict the rotation of the fixed bracket at an appropriate position.
As described above, since the above-described stopper members are not newly attached as separate parts, but they are formed at limited portions of the component parts by serving a double purpose, it becomes difficult for such a stopper member to cause the fixed bracket to be disengaged smoothly from the mounting portion of the vehicle body while restricting the rotation of the fixed bracket by the position of the stopper member during the occurrence of an impact.